DE19638123A1 - Recovery of alcohols from process waste water from silicone resin production - Google Patents

Description

The invention relates to a method for working up the alcohol hol containing waste water, which in the hydrolysis of al koxylated and partially alkoxylated hydrocarbon chlorosila NEN arises. The alcohol is separated off.

Silicone resins consist of spatial networks which are formed from trifunctional or tetrafunctional silicon units R¹SiO _3/2 or SiO _4/2 , where R¹ is selected from aliphatic or aromatic hydrocarbon radicals. In addition, linear units R¹₂SiO and / or monofunctional units R¹₃SiO _{1/2 can be} present. The hydrolysis of trifunctional chlorosilanes or silicon tetrachloride with water leads to a high gel content in the hydrolyzate, even when working in the presence of organic solvents such as toluene and acetone.

Therefore, the one described in DE-A-8 73 433 was introduced very early Resin production from partially alkoxylated chlorosilanes or Al introduced koxysilanes in which the formation of gel fractions is greatly reduced. After hydrolysis falls next to the Resin product an alcohol-containing water phase, which in addition to the from the chlorosilanes hydrochloric acid also silicone resin contains residues and gel components.

To make the resin production economical and for Ab case avoidance, it is of great interest to the deployed Alcohol from the aqueous phase as completely as possible and a fold to regain. The biggest problem with the refurbishment this process stream is the resin and gel components. Will the Alcohol in a still or column distilled out of the mixture, so take on the heat dew after a short time, coverings will grow through growing silicone resin on which hinder the heat transfer and which periodically  must be cleaned. Even when blowing in directly Water vapor forms in the acid from the gel components on the walls.

Another problem when working up the aqueous-alcoholic phase is in many cases the acid, which acts as condensation tion catalyst is necessary. Often because hydrochloric acid forms in the hydrolysis of the partially alkoxylated silanes det, more volatile alkyl halides are formed Heat from the alcohols and from HCl, which in turn emissi cause on problems.

Steam stripping of organically contaminated wastewater is used to remove volatile organic components. In Hwang, Y.-L., the criteria for the successful steam stripping of waste water are: et al .; Ind. Eng. Chem. Res. 1992, 31, 1753-1759 and Hwang, Y.-L. et al .; Ind. Eng. Chem. Res. 1992, 31, 1759-1768 requires a vapor-liquid equilibrium constant at infinite dilution K ^∞ <1 ge. Alcohols have low K ^∞ values, e.g. B. Ethanol -0.4 and methanol -0.5. In Hassan, SQ; J. Air Waste Manage. Assoc., 1992, 42, 936-943, the criterion for the successful implementation of steam stripping is a solubility of the organic component in water of at most 1000 ppm. Steam stripping is therefore completely unsuitable for removing alcohols such as ethanol or methanol from an aqueous solution.

In DD-A-2 28 550 is the recovery of alcohol from the aqueous alcoholic hydrochloric acid used in the manufacture of Methyl silicone resins are obtained by introducing water vapor described. However, it does not describe how the Implementation happens and like that in the hydrochloric acid medium occurring gel deposits and the alkyl chloride emissions ver can be avoided.

The object of the invention was to remove the alcohol from process wastewater To recover silicone resin manufacturing, the emissions of Lower alkyl halides drastically and the buildup on To prevent apparatus parts.

The invention relates to a method for working up the Al alcohol-containing wastewater, which in the hydrolysis of Silanes of the general formula I

R _a 1 SiCl _b OR 2 _4-ab (I),

in the
R¹ are hydrogen atoms or the same or different monovalent, optionally halogen-substituted, SiC-bonded C₁-C₁₈ hydrocarbon radicals,
R² identical or different monovalent C₁-C₁₀ hydrocarbon residues,
a 0, 1, 2 or 3, on average 0.3 to 1.9 and
b 0, 1, 2, 3 or 4, on average 0.0 to 3.0
mean, with the proviso that the sum a + b averages at most 3.5,
for the production of silicone resins, in which the wastewater is made alkaline with alkali in a first step and
in a second step, the alcohol is removed from the resulting alkaline solution or suspension by blowing in steam.

Examples of radicals R 1 are alkyl radicals, such as the methyl, Ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl radical, hexyl radicals, such as the n-hexyl radical, heptylre such as the n-heptyl radical, octyl radicals such as the n-octyl radical and iso-octyl residues, such as the 2,2,4-trimethylpentyl residue, nonyl residues, such as the n-nonyl radical, decyl radicals, such as the n-decyl radical, dodecyl residues, such as the n-dodecyl residue, octadecyl residues, such as the n-octa decyl residue; Alkenyl groups such as the vinyl and allyl groups; Cy cloalkyl radicals, such as cyclopentyl, cyclohexyl, cycloheptyl radicals  and methylcyclohexyl residues; Aryl radicals, such as the phenyl naphtha thyl and anthryl and phenanthryl; Alkaryl residues, such as o-, m, p-tolyl, xylyl and ethylphenyl; Aralkylre such as the benzyl radical, the alpha and the β-phenylethyl radical.

Examples of halogen-substituted radicals R 1 are haloalkyl residues, such as the 3,3,3-trifluoro-n-propyl residue, the 2,2,2,2 ', 2', 2'-hexafluoroisopropyl radical, the heptafluoroisopro pylrest, and haloaryl, such as the o-, in-, and p-chlorophenyl residue.

The unsubstituted radicals R 1 are particularly preferred C₁-C₆ hydrocarbon radicals, especially the methyl and Phenyl radical.

Examples of the radical R² with hydrocarbon radicals 1-10 C atoms are above in the examples of R¹ on ge leads. The radical R 2 is preferably linear and branched te C₁-C₄ hydrocarbon radicals, especially the methyl and Ethyl residue.

The alcohol content of the alcohol-containing wastewater from the Hy drolysis (process wastewater) can vary widely and moves usually at 5 to 50 wt .-%. In the preferred case for the The ethanol content is 15 to 45% by weight.

The silanes of the general formula I can be partially or fully be koxylated, d. H. they can contain chlorine atoms. An on part of preferably at most 10% by weight, in particular maximum At least 2% by weight of the silanes of the general formula I can le only chlorine atoms, but no OR² groups.

In addition to the alcohol that was released from the silanes, can the aqueous phase optionally for hydrolysis and Kon contain used catalyst. Usually it is an acid, in the simplest case it is Hydrochloric acid, if chlorine-containing silanes are used for the hydrolysis were. In this case, the value of b is preferably  on average at least 0.2, preferably at least on average 0.5. Just like the alcohol content, too the acidity varies greatly from 2 to 20 depending on the type of resin % By weight. For the preferred resin manufacturing process partially alkoxylated chlorosilanes is the acid concentration between 10 and 20% by weight.

Responsible for the allocation of apparatus parts is if the process according to the invention is not used, the proportion of silicone resin contained in the process wastewater. The It is in water z. B. in the form of emulsified droplets or as a dispersed, gel-like, voluminous, greasy mas The proportion depends on the type of resin. Genes The amount of gel increases with the proportion of tri or tetra functional silanes. In extreme cases, the amount of gel can be up to 5 vol .-% of the process wastewater.

If resin production in the presence of solvents he follows, traces of it can also be found in the water phase se and in the gel. Solvents can be used with Water have large gaps in the mixture under normal conditions, e.g. B. aliphatic and aromatic hydrocarbons in the boil range up to 250 ° C or esters and ketones with more than 3 C-Ato men. Aromatic hydrocarbons are preferably used fe, particularly preferably toluene and xylene.

Other components present in the process wastewater can be Denaturant from alcohol, which is used to implement the Hydrocarbon chlorosilanes to the silanes of the general Formula I has been used; Impurities over the Starting materials are introduced, e.g. B. saturated or un saturated hydrocarbons from the hydrocarbon chlorine silanes; and alkyl halides formed during alkoxylie tion or hydrolysis from olefins by addition or from the Alcohols through substitution reactions with halogen water Can form acids. The share of these in the Ab components present in water is preferably at most 1% by weight.  

In the first step, the process waste water described above dosed this lye. Both organic and anor ganic bases in pure form or in the form of an aqueous solution solution can be used. Aqueous solutions of Alkali metal hydroxides, in particular sodium hydroxide solution. The Concentration of alkali hydroxide is preferably 20-50 % By weight.

Alkali is preferably added at temperatures of 0 ° C to 40 ° C, especially 10 ° C to 30 ° C and preferably at 0.05 MPa to 1 MPa and continuously. But also different ones Temperatures and pressures or discontinuous additions are not excluded. The dosage is such that the pH of the mixture is at least 8, preferably 11 to 13.

The addition of lye causes extremely rapid condensation of the Resin and gel droplets to insoluble organosilicic acid. This Organosilicic acid is very low in residual groups and has only one low surface energy. It therefore lies on the surface no longer start and can effortlessly in the form of fine particles be filtered.

In contrast, the condensation takes place in the acidic langsa Resins with more residual groups are formed, which slowly grow on all offered surfaces and form coverings, so that it has to be cleaned periodically. Therefore, acidic Work-up also be ensured that the gel fractions in Process wastewater are minimized, which, for. B. by additional Ab cutting devices can be made. This extra effort does not apply to alkaline processing.

The second important effect that the lye has is the Mi minimizing alcohol losses through a substitution reaction with the preferably used hydrohalic acids to Al alkyl halides, which in turn are an important emission pro represent  

The second step is steam stripping. This will be the alka mixture from the first step into a column feeds. Conveniently it is a bubble column oh ne additional internals to make a laying due to resin to avoid particles. Steam is fed in at the same time.

The dosage can be both in cocurrent and in counter electricity. Dosing in countercurrent is preferred Steam feed in the sump and dosing of the alkaline mixture in the upper half of the column. The ratio of Steam and alkaline mixture depends on the alcohol content of the mixture and the energy content of the steam used and can therefore only be given as an example (see Examples).

The mixture of alcohol and what evaporated in the second step It is preferably condensed and is neutral and free of solid and gel components. Only in process wastewater contained solvents may still be present. The Ver ratio alcohol: depending on the conditions in the water Vapor stripping vary widely. Conveniently, it all lies However, at least 1: 2, preferably at least 1: 1.

The residual alcohol content of the In withdrawn from the bubble column content is usually below 1% by weight.

The alcohol-water mixture separated off in the process can suitable process control directly in the resin production be set.

Preferably, the separated alcohol is from what remains completely or partially exempted. It is preferably, for. B. via distillation or separation via a membrane process ren, the alcohol concentrated to 90-100 wt .-% content and then used again in resin production.

In the examples below, if not in each case specified,

• a) all quantities based on weight;
• b) all pressures 0.10 MPa (abs.);
• c) all temperatures 20 ° C.

Examples

A process wastewater from the was used for the examples Production of methyl silicone resin with the following composition:

Example 1:

The process wastewater was adjusted to pH with aqueous NaOH (25% by weight) 12 set. A bubble column (⌀ 100 mm, length 2000 min, du ran glass) was filled to 60% with the process wastewater. The Process wastewater could continuously by means of a membrane pump pe be dosed at the level of the liquid. In the swamp was also able to do this continuously using a diaphragm pump process wastewater depleted of alcohol is withdrawn. 100 mm above the sump fume was steam with egg over a nozzle ner temperature of 160 ° C fed. The steam ratio: Process wastewater was 0.9. The dosing of the process wastewater was 3 kg / h.  

The distillate consisted of:

The sump fume contained fine particles of methyl silica and 0.8 wt% ethanol. After 100 h, the glass column was without a topping.

Only the amount of ethyl chloride already present was found no new formation took place.

Example 2 (comparative example)

Example 1 was repeated, but the process waste water not pretreated. It started after just a few hours to form a coating on the glass. At the end of the test The sump discharge line was 100 h to almost half of the cross overgrown and had to be cleaned. The Swampab train contained a few, irregularly large parts of methyl silicic acid particles from flaking off wall coverings and 0.9% by weight ethanol.

The distillate consisted of:

There was new formation of ethyl chloride.

Claims (6)

1. Process for working up the alcohol-containing waste water, which in the hydrolysis of silanes of the general formula I R _a ¹SiCl _b OR² _4-ab (I), in the
R¹ are hydrogen atoms or the same or different monovalent, optionally halogen-substituted, SiC-bonded C₁-C₁₈ hydrocarbon radicals,
R² identical or different monovalent C₁-C₁₀ hydrocarbon residues,
a 0, 1, 2 or 3, on average 0.3 to 1.9 and
b 0, 1, 2, 3 or 4, on average 0.0 to 3.0
mean, with the proviso that the sum of a + b is a maximum of 3.5, for the production of silicone resins, in which the waste water is made alkaline with alkali in a first step and
in a second step, the alcohol is removed from the resulting alkaline solution or suspension by blowing in steam. 2. The method according to claim 1, wherein R¹ is a methyl or Phenyl radical means. 3. The method of claim 1 or 2, wherein R² is a methyl or ethyl radical. 4. The method according to any one of claims 1 to 3, wherein the Alcohol content of the alcohol-containing wastewater from Hy drolysis is 5 to 50 wt .-%. 5. The method according to any one of claims 1 to 4, in which he step as an alkali, an aqueous solution of Alka lihydroxid is used.   6. The method according to any one of claims 1 to 5, in which he the first step with the lye is a pH value of the waste water at least 8 is set.